It has been proposed to provide panel assemblies having hidden fastening systems. For example, Guzzo, in U.S. Pat. No. 3,852,933, utilises undulating roof panels with separate clips for holding the panels. The panels are not unitary panels including their own fastening flanges through which fasteners are passed. Furthermore, the panels are not rigidly fixed together but are interlocked by manipulation to prevent accidental separation.
In U.S. Pat. No. 1,376,751, Edwards discloses the use of a roofing cleat to prevent crushing or bending of panels when a nail is driven through the panels. The cleats are thus intended to overcome the disadvantages which arise when fixing panels in a conventional manner, that is by driving nails right through the panels.
It is quite clear that Edwards' roofing system and his various panels are totally unsuited to a hidden fastening system.
Roys in U.S. Pat. No. 95,732 has one panel nailed to a structure and another panel is slid over the fastened panel to secure the two panels together. There is no space between the panels for heads of fasteners other than nails, such as bolt heads. In practice, this structure would apparently be impractical because of the difficulties of sliding one panel over another and a sliding engagement would probably also make it impractical, if not impossible, to include conventional sealants between the ribs. In addition it seems that the ribs could be trodden down relatively easily by people walking on the roofing. This could make subsequent separation of the panels virtually impossible without completely destroying the panels.
Moomaw, Stasch and Johnson in U.S. Pat. Nos. 1,329,794, 841,276 and 3,495,363, provide hidden fastening systems with interlocking panels. In each case, the panels are of a relatively complex shape. Stacking of the panels for transport purposes would clearly be difficult and could readily result in damage to the panels.
Stasch and Moomaw both use nails to fix down their panels and there is no provision for the use of other fasteners, such as bolts. The panels are forced together or manipulated in order to interlock the panels.
Selph, in U.S. Pat. No. 2,112,178, discloses an anchor lock for use in metal roofing having hidden fasteners. Clearly the use of an anchor lock will not ensure that the overlapping ridges are drawn tightly together in practice and cannot prevent excessive free play between the panels. This type of lock would also make it difficult to compress a sealant between the panels.
In Selph's panels, the lugs are pre-attached and the holes are formed in the panels before use and it is readily apparent this would give rise to difficulties in obtaining exact alignment of the panels during assembly. Furthermore, it would make it difficult to stack the sheets without damaging the lugs. In practice, it would probably also be difficult to attach the lugs without causing some damage to the panels themselves.
Once the roofing had been fixed in place, relative movement between Selph's ridges could serve to sever the lugs from the panel.
In Australian Pat. No. 257,361, Handford shows a panel with edge ridges of basically rectangular outline. These ridges are provided with resiliently interlocking portions which hold the ridges together. In FIGS. 2 and 4, a hidden fastener arrangement is used but this is based on a fastening with the attachment zones placed a considerable distance from the structure. In FIGS. 3 and 5, a locating bracket has to be used to attach the ridges to the structure.
In Australian Pat. No. 226,784, Pelman discloses a hidden fastener system which is dependent on a bracket fixed to a structure and hooking over the edge of a lower panel. An upper panel hooks over the bracket by means of lip 17 and is thus located in place. The clips must clearly be accurately pre-located at a spacing which is equal to the distance between the ridges of each panel. There is no provision for ensuring that the upper panel does not separate from the bracket and there is no practical way of locating conventional sealant strips between the panels.